Renin
Renin ( ), also known as angiotensinogenase is an enzyme that participates in the body's renin-angiotensin system (RAS) that mediates extracellular volume (i.e. that of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction. Thus it regulates the body's mean arterial blood pressure. Discovery Renin was discovered, characterized and named in 1898 by Robert Tigerstedt, Professor of Physiology at the Karolinska Institute in Stockholm. Biochemistry and Physiology Structure The primary structure of renin precursor consists of 406 amino acids with a pre- and a pro- segment carrying 20 and 46 amino acids respectively. Mature renin contains 340 amino acids and has a mass of 37 kDa. Secretion The peptide hormone is secreted by the kidney from specialized cells called granular cells of the juxtaglomerular apparatus in response to: *A decrease in arterial blood pressure (that could be related to a decrease in blood volume) as detected by baroreceptors (pressure sensitive cells). This is the most causal link between blood pressure and renin secretion (the other two methods operate via longer pathways). *A decrease in sodium chloride levels in the ultra-filtrate of the nephron. This flow is measured by the macula densa of the juxtaglomerular apparatus. *Sympathetic nervous system activity, that also controls blood pressure, acting through the β1 adrenergic receptors. Human Renin is secreted by at least 2 cellular pathways: a constitutive pathway for the secretion of prorenin and a regulated pathway for the secretion of mature renin. The Renin-Angiotensin-Aldosterone Axis / Renin-Angiotensin System (RAS) , showing role of renin at bottom.Page 866-867 (Integration of Salt and Water Balance) and 1059 (The Adrenal Gland) in: ]] *''Mechanism of action of Renin:'' The enzyme circulates in the blood stream and breaks down (hydrolyzes) angiotensinogen secreted from the liver into the peptide angiotensin I. *''Rest of the RAS:'' Angiotensin I is further cleaved in the lungs by endothelial-bound angiotensin converting enzyme (ACE) into angiotensin II, the most vasoactive peptide. Brenner & Rector's The Kidney, 7th ed., Saunders, 2004. pp.2118-2119.Full Text with MDConsult subscription Angiotensin II is a potent constrictor of all blood vessels. It acts on the musculature and thereby raises the resistance posed by these arteries to the heart. The heart, trying to overcome this increase in its 'load', works more vigorously, causing the blood pressure to rise. Angiotensin II also acts on the adrenal glands and releases Aldosterone, which stimulates the epithelial cells in the distal tubule and collecting ducts of the kidneys to increase re-absorption of salt and water, leading to raised blood volume and raised blood pressure. The RAS also acts on the CNS to increase water intake by stimulating thirst, as well as conserving blood volume, by reducing urinary loss through the secretion of Vasopressin from the posterior pituitary gland. The normal concentration in adult human plasma is 1.98-24.6 ng/L in the upright position.Hamilton Regional Laboratory Medicine Program - Laboratory Reference Centre Manual. http://lrc.stjoes.ca/detail.asp?RecNumber=723&TestFind=renin&SortBy=Name&ViewAlpha=&ParNum= Function Renin activates the renin-angiotensin system by cleaving angiotensinogen, produced by the liver, to yield angiotensin I, which is further converted into angiotensin II by ACE, the angiotensin-converting enzyme primarily within the capillaries of the lungs. Angiotensin II then constricts blood vessels, increases the secretion of ADH and aldosterone, and stimulates the hypothalamus to activate the thirst reflex, each leading to an increase in sodium retention and blood pressure. Renin is secreted from juxtaglomerular cells (of the afferent arterioles), which are activated via signaling (the release of prostaglandins) from the macula densa, which respond to the rate of fluid flow through the distal tubule, by decreases in renal perfusion pressure (through stretch receptors in the vascular wall), and by nervous stimulation, mainly through beta-1 receptor activation. A drop in the rate of flow past the macula densa implies a drop in renal filtration pressure. Renin's primary function is therefore to eventually cause an increase in blood pressure, leading to restoration of perfusion pressure in the kidneys. Renin can bind to ATP6AP2, which results in a fourfold increase in the conversion of angiotensinogen to angiotensin I over that shown by soluble renin. In addition, renin binding results in phosphorylation of serine and tyrosine residues of ATP6AP2. Genetics The gene for renin, REN, spans 12 kb of DNA and contains 8 introns. It produces several mRNA that encode different REN isoforms. Clinical applications An over-active renin-angiotension system leads to vasoconstriction and retention of sodium and water. These effects lead to hypertension. Therefore, renin inhibitors can be used for the treatment of hypertension.Presentation on Direct Renin Inhibitors as Antihypertensive Drugs This is measured by the plasma renin activity (PRA). In current medical practice, the renin-angiotensin-aldosterone-System's overactivity (and resultant hypertension) is more commonly reduced using either ACE inhibitors (such as ramipril and perindopril) or angiotensin II receptor blockers (ARBs, such as losartan, irbesartan or candesartan) rather than a direct oral renin inhibitor. ACE inhibitors or ARBs are also part of the standard treatment after a heart attack. See also * Renin inhibitor * Angiotensin-converting enzyme * plasma renin activity. References External links * * Category:EC 3.4.23 Category:Hormones of the kidneys Category:Peptide hormones Category:Renal physiology ar:رينين cs:Renin de:Renin dv:ރީނިން es:Renina fa:رنین (آنزیم) fr:Rénine it:Renina he:רנין nl:Renine ja:レニン no:Renin pl:Renina pt:Renina ru:Ренин simple:Renin sr:Ренин fi:Reniini sv:Renin uk:Ренін zh:肾素 -->